code: def test_empty_count_window() -> None:
      df = pl.DataFrame(
          {"ID": [], "DESC": [], "dataset": []},
          schema={
              "ID": pl.String,
              "DESC": pl.String,
              "dataset": pl.String,
          },
      )
  
      out = df.select(pl.col("ID").count().over(["ID", "DESC"]))
      assert out.schema == {"ID": pl.UInt32}
      assert out.height == 0
  
file_path: polars/py-polars/tests/unit/test_empty.py
imports: import pytest
  import polars
  from polars.testing import assert_frame_equal, assert_series_equal
label_desc: Use image node_id 6 for calling a global function with example usage: test_empty_count_window() without return types